[mkgmap-dev] Sea generation

Thu Nov 4 20:14:36 GMT 2010

Op 04-11-10 20:24, Marko Mäkelä schreef:
> On Thu, Nov 04, 2010 at 08:06:18PM +0100, Lambertus wrote:
>> So I'm looking forward to any improvements that work without
>> hand-picking tile borders.
> You are cutting a planet extract yourself, aren't you?
Yes, with Splitter in automatic mode (no areas.list)
>   My problems are
> different, because I am relying on an area extract that is not
> rectangular and lacks information of the bounding polygon.
Ah, ok, I wasn't aware of that.
>   You could be
> suffering from bad data. You know, I have been told that the sea areas
> on the Mapnik rendition are based on some fixed data and the
> natural=coastline lines are ignored.
That rings a bell, but I hadn't connected the dots...
>   It is relatively easy to keep a
> small area free from mkgmap-reported issues. Usually there are fewer
> than 5 errors when I do a test build, and after fixing the issues, the
> next day I typically get an error-free map. For any bigger area, I guess
> you can never get a mkgmap-complaint-free map, not even if you had the
> resources to fix all the reported errors by the time the next day's
> extract is cloned off.
Indeed, I see lots of errors in Mkgmap output. I don't think a single 
person can fix them in time before the next planet dump (which probably 
will have new errors).
> I have been toying with the idea of hand-picking tile borders for
> Estonia as well, but I don't know if it is worth my trouble. I'd guess
> that the country extract (as opposed to an Europe or planet extract) is
> most useful for islands. Finland is an island in some sense: you can't
> cross the Russian border without a passport and visa, the land borders
> to Sweden and Norway in the north are very far away from most of the
> population, and you will have plenty of time to switch maps when
> crossing the sea borders. Sweden, Norway and Estonia are less of
> islands, because they have easily crossable land borders. The map would
> have to lump several countries together in order to be practical, and I
> don't want to start downloading and cutting the Europe extract.
Ok it dawns on me that Finland can be a special island case. But my 
ultimate wish (which many of you will probably share) is that it all can 
be done in hands-off automatic mode. Like I said before hand-picking 
tile-borders in a quickly changing OSM environment is a daunting task 
and I rather just not use functionality then make my life overly 
complex. :-) But anyway, displaying the sea in the maps would still be 
awesome.
> When it comes to incomplete multipolygons that are severed by the tile
> borders, I guess that mkgmap should just ignore incomplete polygons that
> are totally outside the bounding box. Maybe this has been implemented
> already, because I am seeing very few multipolygon warnings nowadays. I
> should check if there is anything wrong about the two multipolygons that
> mkgmap now complains about near the tile borders.
>
Would it be possible to close the polygons in Mkgmap? I realise such 
would not be easy, but maybe someone has an idea?

Thanks for your clarifications!